The present invention relates to a multi-layered sintered sliding member comprising a back metal composed of a steel plate and a sintered alloy layer formed integrally by securing on the surface of the back metal.
Heretofore, as the multi-layered sintered sliding member, for example, Japanese Patent Application Laid-Open (KOKAI) 50-150656 discloses a multi-layered sintered sliding member formed by bonding a sintered copper alloy layer to a back metal composed of a steel plate, in which the sintered alloy and the back metal are firmly secured without oxidizing a surface of the back metal by mixing an element or compound having a great standard energy for the oxidizing reaction as compared with iron in the ingredients of the sintered alloy, for example, zinc, cadmium, silicon, magnesium, aluminum or calcium silicide; and Japanese Patent Publication 56-12288 discloses a multi-layered sintered sliding member formed integrally by bonding a thin steel plate secured integrally with a sintered copper alloy layer containing at least 3% by weight of graphite dispersed therein as a lubricating material, on a thick steel plate by means of a thin phosphorbronze alloy plate.
However, since the multi-layered sintered sliding member of Japanese Patent Application Laid-Open (KOKAI) 50-150656 contains metal elements such as zinc, cadmium and silicon in the sintered alloy, the application range of the sliding member is inevitably limited and, particularly, in such an application use as a great load and impact load are intermittently exerted, for example, sliding portions of a press machine or press die, or floor plates for slidingly supporting tongue rails of a railway track point portions, plastic deformation is brought about by such load to the sintered alloy layer, and as a result, there arises a problem that the member can not be applied to the application use described above.
On the other hand, although the multi-layered sintered sliding member of Japanese Patent Publication 56-12288 is remarkably improved with the load resistance and impact resistance as compared with the sliding member of Japanese Patent Application Laid-Open (KOKAI) 50-150656, there are a problem that plastic deformation occurs in the sintered layer in the above-mentioned application use and an economical problem that the production process is complicate, thereby increasing the cost.
It has been demanded to supply a multi-layered sintered sliding member which can be used in severe conditions where great load and impact load are intermittently exerted, and which can be produced at a low cost by simplifying the production process.
As a result of the present inventors' earnest studies for overcoming the foregoing drawbacks, it has been found that by securing a sintered alloy layer on the surface of a back metal composed of a steel plate having protrusions on the surface, in which the sintered alloy layer is composed of a low density alloy region and a high density alloy region, the obtained multi-layered sintered sliding member can slidingly support the high load and impact load without causing plastic deformation against such loads. The present invention has been attained based on this finding.